Ice Cream Defects
If you haven't already done so, check out the Milk Grading and Defects section for a mini-introduction to the senses. This section will cover the following topics:
Can be classified according to the flavouring system (lacks flavour or too high flavour, unnatural flavour), the sweetening system (lacks sweetness or too sweet), processing related flavour defects (cooked), dairy ingredient flavour defects (acid, salty, old ingredient, oxidized/metallic, rancid, or whey flavours), and others (storage/absorbed, stabilizer/emulsifier, foreign). Some details are given below.
Flavoring System
Unnatural flavor - Caused by using flavours that are not typical of the designated flavour i.e. wintergreen flavour on vanilla ice cream. esp. vanillin
Egg: Caused by using too much egg in an ice cream that is not specified as a custard ice cream - resembles French vanilla ice cream .
Processing
Cooked: Caused by using milk products heated to too high a temperature or by using excessively high temperatures in mix pasteurization. It can dissipate with time, the same as cooked defect in fluid milk. Sulfhydryl flavor: Caramel-like, scalded milk, oatmeal-like.
Dairy Ingredients
High Acid: Use of dairy products with high acidity (usually due to bacterial spoilage) or holding mix too long and at too high a temperature before freezing. Acid/sour flavours are more rare these days due to the growth of proteolytic psychrotrophs during storage at elevated temperatures, rather than lactic acid bacteria.
Salty: Ice cream too high in milk solids-not-fat. Too much salt may have been added to the mix. High whey powder, or maybe salted butter used instead of sweet butter.
Old Ingredient: Caused by the use of inferior dairy products in the preparation of the mix. Powders made from poor milk or stored too long at elevated temperature or butter made from poor cream will contribute to old ingredient flavour. Unpleasant aftertaste.
Oxidized: Caused by oxidation of the fat or lipid material such as phospholipid, similar to fluid milk oxidation. Induced by the presence of copper or iron in the mix or from the milk itself. Mono-and-di-glyceride or Polysorbate 80 can also oxidize. Various stages - cardboardy, metallic (also described as painty, fishy).
Rancid: Caused by rancidity (high level of free butyric acid from lipolysis) of milk fat. May be due to use of rancid dairy products (pumping or excessive foaming of raw milk or cream) or to insufficient heat before homogenization of mix. See description of Lipolysis, especially the release of free butyric acid.
Others
Storage: Usually develops from "Lacks Freshness" and is most pronounced on ice cream which have been held in a stale storage atmosphere. Ice cream can also pick up absorbed volatile flavours from the storage environment (e.g., paint, ammonia, or in dipping cabinets - volatiles from nearby flavours.
1. Coarse/Icy Texture: Due to the presence of ice crystals of such a size that they are noticeable when the ice cream is eaten. See ice cream structure, the freezing aspects of ice cream manufacturing, ice cream freezing theory, and ice cream shelf life. May be caused by:
- Insufficient total solids (high water content).
- Insufficient protein.
- Insufficient stabilizer or poor stabilizer.
- Insufficient homogenizing pressure (due to its effect on fat structure formation).
- Insufficient aging of the mix (stabilizer hydration, also fat crystallization and development of resulting fat structure).
- Slow freezing because of mechanical condition of freezer.
- Incorporation of air as large cells because of physical characteristics of mix or type of freezer used.
- Slow hardening.
- Fluctuating storage room temperatures.
- Rehardening soft ice cream.
- Pumping ice cream too far from continuous freezer before hardening.
- Fluctuating temperatures during storage and distribution - the most likely cause! See discussion of ice cream shelf life.
2. Crumbly Body: A flaky or snowy characteristic caused by:
- High overrun together with large air cells.
- Low stabilizer or emulsifier.
- Low total solids.
- Low protein.
3. Fluffy Texture: A spongy/marshmallowy characteristic caused by:
- Incorporation of large amount of air.
- Low total solids.
- Low stabilizer content.
4. Gummy Body: This defect is the opposite of Crumbly in that it imparts a pasty or putty-like body. It is caused by:
- Too low an overrun.
- Too much stabilizer.
- Poor stabilizer.
5. Sandy Texture: One of the most objectionable texture defects but easiest to detect. It is caused by Lactose crystals, which do not dissolve readily and produce a rough or gritty sensation in the mouth. This can be distinguished from "iciness" because the lactose crystals do not melt in your mouth. This defect can be prevented by many of the same factors that inhibit iciness:
- hardening the ice cream quickly
- maintaining low storage room temps.
- preventing temperature fluctuations...from manufacturer to consumer
Lactose crystal formation is further discussed in the Dairy Chemistry and Physics section.
6. Weak Body: Ice cream lacks "chewiness" and melts quickly into a watery liquid. Gives impression of lacking richness. May be caused by:
- Low total solids.
- High overrun.
- Insufficient stabilizer.
1. Curdy Melt-Down: May be due to visible fat particles or due to coagulation of the milk proteins so is affected by factors that influence fat destabilization or the protein stability such as:
- High acidity (protein coagulation).
- Salt balance (protein coagulation).
- High homogenizing pressures (fat coagulation).
- Over-freezing in the freezer (fat coagulation).
2. Does not Melt: See ice cream structure, under the section on melt-down and fat structure/destabilization. May be caused by:
- Over emulsification.
- Wrong emulsifier.
- High fat.
- Excessive fat clumping in the mix due to homogenization at too low a temperature or single-stage homogenizer.
- Freezing to too low a temperature at freezer.
3. Wheying off: The salt balance, protein composition, and carrageenan addition (or lack or it) all are factors.
1. Colour Uneven: Applies usually to ice cream in which colour has been used, but may be noticed in vanilla ice cream under some circumstances.
2. Colour Unnatural:
- Wrong shade of color used for flavoured ice cream.
- Too much yellow coloring used in vanilla ice cream.
- Grayish color due to neutralization.
A very troublesome defect in ice cream since there appears to be no single cause or remedy. Defect shows up in hardened ice cream and manifests itself in reduced volume of ice cream in the container usually by pulling away from the top and/or sides of container. Structurally, it is caused by a loss of spherical air bubbles and formation of continuous air channels. Some factors believed associated with the defect are:
- Freezing and hardening at ultra low temperatures.
- Storage temperature. Both low and high appear to contribute.
- Excessive overruns.
- Pressure changes, for example, from altitude changes (lids popping when shipped to high altitudes, shrinkage when returned to low altitudes).
NOTE:
Retailing: More so than other frozen products, ice cream requires constant, uninterrupted freezing cycle at low temperatures to avoid problems.
Problems at retail level can arise from overfilling of display cabinet, heat from display lamps or door defrosters, hot air from incorrectly positioned circulation fans, displaying ice cream together with semi-frozen goods.
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